How would NIR work across a shared imaging system, if Trust A "pulls" the image then Trust B also try to pull the same image would it create another copy on the system?

This would be subject to the supplier’s discretion in terms of how this behaviour is handled in their system, however both suppliers and trust should be aware of the governance aspects of NIR including the duplicate policy. https://digital.nhs.uk/services/national-imaging-registry/governance